The invention relates to an optically active form of a pyridyl-4H-1,2,4-oxadiazine derivative, to the therapeutical use thereof and to pharmaceutical compositions containing the compound as active ingredient. More particularly, the invention relates to the (xe2x88x92) enantiomer of 5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine and its acid addition salts as well as the use of these chemical compounds in the treatment of vascular diseases and pharmaceutical compositions containing the said compounds as active ingredients.
The racemic 5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine is known. Its preparation and hsp expression enhancing effect on cells exposed to heat shock is described in WO 97/16349 and its protective and regenerating effect on vascular endothelial cells is described in WO 98/06400. This compound is suitable mainly for fending off the damages caused by ischemia and in the treatment of cardiovascular and cerebrovascular diseases.
The optically active forms of 5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)-4H-1,2,4-oxadiazine were not described in the literature.
During our recent experiments, the optically active forms of 5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine were prepared and their biological activities studied. It has been found that the (xe2x88x92)-5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine has a substantially stronger vasoprotective and cardioprotective effect than the (+) enantiomer and the racemic compound. It is expressly more efficient in preventing the damages of the endothelium caused by ischemia.
Due to these properties the (xe2x88x92)-5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine is prominently suitable to the treatment of vascular diseases and diseases connected to vascular abnormalities.
In course of experiments we recognized, unexpectedly, that (xe2x88x92)-5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine, in contrast to the (+)-enantiomer and the racemic compound, has a positive inotropic effect i. e. it is capable of increasing the contractile force of the heart. This activity makes (xe2x88x92)-5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine suitable for the treatment of patients with cardiac failure, contrary to the (+)-enantiomer and the racemic compound, the application of which being risky in case of cardiac failure.
The above mentioned advantageous biological properties of (xe2x88x92)-5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)-4H-1,2,4-oxadiazine are verified in the following tests.
Langendorff Perfused Rat Heart
Protocol for Assesment of Endothelial Function Before and After Ischemia
Rats were heparinised with i.p. heparin sodium (2500 IU) and anesthetized with i.p. pentobarbital (60 mg/kg). Hearts from spontaneously hypertensive (SH) rats were quickly removed and immediately perfused via the aorta using a gravity-flow, non-recirculating Langendorff apparatus (Experimetria Ltd) at a constant perfusion pressure (100 cm H2O) with Krebs-Henseleit Solution (KHS) containing in mM: NaCl 120; KCl 5.4; CaCl2 2.7; MgCl2 1.1; NaHCO3 24; D-glucose 11. The KHS was gassed with carbogen (95% O2; 5% CO2) resulting pH 7.4.
We used the so-called non-working heart model and measured the mean coronary flow by a transonic flow meter (Type T206, Transonic Systems Inc.). The flow probe was placed above the aortic cannula. Coronary flow was monitored throughout the experiment and registered by a potentiometric recorder. Hearts were allowed to beat spontaneously throughout the experiment. After 20-30 min of equilibration period the coronary flow reached a baseline value.
Endothelial function was assessed through observations of preischemic and postischemic coronary flow responses to serotonin (5-HT). In response to serotonin, the progress of dilatation of coronary artery depends on the soundness of the endothelium.
The Langendorff infusion was switched to the another column containing additional 10xe2x88x927 M serotonin (5-HT, Sigma Chemical Co.). The ensuing dilatation of coronary artery was monitored and when the steady state had been reached the 5-HT was washed out by switching back to the ordinary KHS. The heart was then subjected to a global ischemia for 10 min by the clamping the aortic cannula. At the end of the ischemic period, the heart was reperfused. When the baseline coronary flow had been reestablished, the heart was again subjected to the same protocol of sequential infusion of 5-HT and KHS as in the preischemic period. Control hearts were perfused with pure KHS and the hearts of the another three groups were perfused with KHS containing additional 10xe2x88x926 M racemic 5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine, (xe2x88x92)-5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine and (+)-5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine, respectively. 20-30 min after the onset of hemodynamic stability, perfusion of the drugs were initiated and continued until reperfusion with the exception of the occlusion period.
The results are shown in the following table. The potischemic coronary responses are expressed in percentage of the preischemic vasodilator responses.
Perfusion of the rat heart with the (xe2x88x92)-5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine (10xe2x88x926 M) preserved endothelial function after 10 min of global ischemia in contrast with the racemic compound, the (+) enantiomer and the racemic compound or the SH control.
Myocardial Infarction in Spontaneously Hypertensive Rats
Induction of Infarction
Myocardial ischemia was induced by a temporary occlusion of the main left coronary artery, according to Griswold et al (J. Pharmacol. Methods 1988, 20: 225-235). SH rats were anaesthetized with sodium pentobarbital (60 mg/kg i.p.). After tracheotomy, the animals were ventilated with room air by a respirator for small rodents (model: Harvard 552), with a stroke volume of 1,5-2 ml/100 g and a rate of 55 strokes/min to maintain normal pO2, pCO2 and pH parameters. The right carotid artery was catheterized and connected to a pressure transducer (P236B Stetham) for the measurement of systemic arterial blood pressure (BP) by means of a preamplifier (Hg-O2D Experimetria(copyright)). Heart rate (HR) was measured by a cardiotachometer (HR-01, Experimetria(copyright)). The electrocardiogram (ECG standard lead III) was recorded on a devices recorder (ER- 14, Micromed(copyright)) by means of subcutaneous steel needle electrodes. The chest was opened by a left thoracotomy and the heart was exteriorized by a gentle pressure on the right side of the rib cage. A 4/0 silk ligature was quickly placed under the main left coronary artery. The heart was replaced in the chest and the animal left to recover. Rectal temperature was monitored and was maintained constant at 37xc2x0 C. The experiment was initiated with a 15 min stabilization period during which the observation of a sustained blood pressure less than 70 mmHg and/or the occurrence of arrhythmias lead to exclusion. Myocardial ischemia was induced with coronary artery occlusion for 1 h and reperfusion allowed for 1 hour. The drugs were administered orally 6 hours before occlusion.
Quantification of Myocardial Infarction
At the end of experiment, the heart was quickly removed. The left ventricle was then sliced into 2 mm thick sections parallel to the atrioventricular groove. The slices were incubated in a 0.1% solution of p-Nitroblue Tetrazolium (NBT) grade III, pH 7,4 for 15 min. The non-infarcted area was colored blue due to formation of a precipitate that results from reaction of NBT with dehydrogenase enzymes. Loss of these enzymes in the infarcted myocardium prevents the formation of the precipitate; thus, the infarcted area within the risk region remains pale yellow. The necrotic area was determined using computerized image analysis (COLIM, Pictron Kft), and was expressed as a percentage of the left ventricle.
Results
Acute single oral treatment with the (xe2x88x92) enantiomer (100 mg/kg) 6 hours before occlusion significantly reduced myocardial infarct size and increased survival rate in contrast with the (+) enantiomer in SH rats. It could be stated that the (xe2x88x92) enantiomer was more active in this model than the racemic compound or the (+) enantiomer.
Effect of racemic 5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine and its (xe2x88x92) and (+) enantiomers on the contractile force of heart
Materials and Methods
New Zealand white rabbits (male, 2-3 kg) were killed by a blow on the nape. The hearts were rapidly removed after opening the chest. Right ventricular papillary muscles were dissected and mounted in organ holding chambers and pre-tension of 0.5 g was applied. The superfusate contained (in mM) 120 NaCl, 5.4 KCl, 2.7 CaCl2, 1.1 MgCl2, 1.1 NaH2PO4, 24.0 NaHCO3 and 11.0 glucose. The pH of this superfusate was 7.4 at 37xc2x0 C. when gassed with 95% O2 and 5% CO2. Stimulation and measurements were carried out by Isosys System of Experimetria, Budapest, Hungary. The preparations were paced by 1-ms-wide isolated constant voltage at a cycle length of 1000 ms. The amplitudes of the pulses were equal to twice as high as the diastolic threshold value, delivered through a pair of platinum electrodes. Before the start of the measurements the preparation was equilibrated for 60 min to allow the stabilization of its mechanical parameters. The drugs were added to the organ bath cumulatively, without washing out. Period of the incubation was 15-20 min. Measured parameters were: resting force (mg) and changes in the amplitude of contractile force (mg) which was expressed in % of the control.
Results
The (xe2x88x92)-5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine has a positive inotropic effect in rabbit papillary muscle between 10xe2x88x926 and 10xe2x88x924 molar range, the (+) enantiomer and the racemic compound showed a negative inotropic effect. Depression of left ventricular contractility is an unwanted effect sufficient to contraindicate its use in patients with overt cardiac failure.
The (xe2x88x92)-5,6dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine can be prepared from the racemic compound. The racemic compound can be prepared for example by halogenating N-[2-hydroxy-3-(I-piperidinyl)-propoxy]-3-pyridine-carboximidamide and ring closure of the halogenated compound. In the first step the said starting compound is reacted with an inorganic halogenating agent, preferably thionyl chloride optionally in an inert solvent, and the excess of the reagent is removed for example by evaporation. The N-[2-halo-3-(1-piperidinyl)-propoxy]-3-pyridine-carboximidamide thus obtained is (optionally after isolation and purification) cyclised with a strong base, for example potassium tert. butylate, resulting in the desired racemic 5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine.
The resolution of the racemic compound can be accomplished by forming diastereomer salts. Preferably optically active (xe2x88x92)-L-dibenzoyl tartaric acid is used for the resolution. The salts are formed in an appropriate polar solvent, preferably methanol or in a mixture of methanol and water then the isolated salt enriched in the desired diastereomer is recrystallized from the same or a similar solvent for further purification. The progress of purification is expediently monitored by HPLC chromatography with use of a chiral sorbent. When the desired purity is attained the base is liberated simply by alkalinization or alkaline extraction and isolated by recrystallization.
The (xe2x88x92)-5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)AH-1,2,4-oxadiazine thus obtained can be used as a base or optionally can be converted into an acid addition salt appropriate to the particular application. For this purpose the base is reacted with an inorganic or organic acid in a known manner. The (xe2x88x92)-5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine base and the acid addition salts are one of the objects of the invention.
According to the invention these compounds are used in the treatment and prevention of vascular diseases and diseases connected to vascular abnormalities.
According to a special embodiment of the invention these compounds are applied in the treatment and prevention of vascular diseases and diseases connected to vascular abnormalities on patients with cardiac failure.
The compounds of the invention can be used both in the human therapy and in the veterinary practice.
Accordingly, in a further aspect, the invention relates to a method of treatment and prevention of vascular diseases and diseases connected with vascular abnormalities comprising administering to the patient (xe2x88x92)-5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine or an acid addition salt thereof. In a preferred embodiment case of the invention, (xe2x88x92)-5,6-dihydro-5-(1-piperidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine or an acid addition salt thereof is administered to a patient suffering in cardiac failure.
The dose of the compounds of the invention depends on the patient and the disease and varies from 0.1 to 200 mg/kg/day, preferably from 0.1 to 50 mg/kg/day. For human therapy the preferred oral dose is 10-200 mg, in case of rectal administration 1-15 mg and in case of parenteral treatment 2-20 mg for an adult daily. These doses are applied in unit dosage forms optionally distributed to 2-3 administrations, particularly in case of oral treatment.
The invention relates further to the pharmaceutical compositions usable to the treatment. The parmaceutical compositions of the invention comprise (xe2x88x92)-5,6-dihydro-5-(1-pipenidinyl)-methyl-3-(3-pyridyl)4H-1,2,4-oxadiazine or an acid addition salt thereof as active ingredient with carriers and auxiliary materials conventionally used in the pharmaceutical compositions.
The compositions of the invention can be formulated in solid or liquid forms usually applied in the human and veterinary therapy. For oral use tablets, coated tablets, dragees, granules, capsules, solutions or syrups, for rectal administration suppositories and for parenteral administraton lyophilised or non-lyophilised injectables or infusion solutions can be prepared with use of known ways of preparation. The oral compositions may comprise fillers such as microcrystalline cellulose, starch, lactose, lubricants, such as stearic acid and magnesium stearate, coating materials such as sugar, film materials such as hydroxymethyl cellulose, flavours or sweeteners such as methyl paraben and saccharine and colorants. The auxiliaries in suppositories may be for example cocoa bufter and polyethylene glycol. The compositions for parenteral use may comprise saline or optionally dispersing and wetting agents such as propylene glycol with the active ingredient.